In recent years, as one of efforts to preserve the global environment and suppress the generation of greenhouse gas emissions, electric vehicles with less environmental impact have been spreading instead of gasoline engine vehicles.
In a case of an electric vehicle, its power source is configured by a combination of storage batteries and an electric motor and basically, the electric vehicle must be supplemented with electric power from an external battery charger. For this reason, there are required measures for suppressing the consumption of stored power in the electric vehicles. Among the measures, it is the most effective means to suppress the power consumption for heating (i.e. air conditioner) whose power consumption is large.
Therefore, it has been proceeded to adopt means for directly transferring warmth to an occupant (driver) through a steering wheel that is directly touched by the occupant (driver). As one of such means, there is known a configuration where a heater wire as a heating element is embedded in a steering wheel.
Specifically, there is known a configuration that suppresses the use of a heater apparatus while reducing the operational difficulty or discomfort caused by the coldness of the steering wheel when starting and driving an electric vehicle that has been parked, for example, outdoors in winter, by assembling a heater unit into a steering wheel and additionally heating the steering wheel even when various institutions are not sufficiently warmed in a vehicle that has just started.
As a conventional steering wheel provided with such a configuration, there is known, for example, a method of forming a steering wheel rim having a heater wire embedded therein, the method includes: preparing a core metal including a rim core part and a cylindrical spacer for covering the rim core part; hooking a heater wire around the spacer in a zigzag manner or the like; setting the spacer in a cavity of a molding die while being held in the cavity through the heater wire; and injecting a synthetic resin material, such as urethane, into the molding die, thereby triggering a reaction of the synthetic resin material in the cavity of the molding die to form a resin layer covering the heater wire (see JP 2013-139203 A).
As another conventional steering wheel, there is also known a steering wheel in which a heater wire supported on a sheet-like base material is wound around a rim core part directly and further covered with a resin layer (see JP 2015-189294 A).